1. Field of the Invention
The present invention relates to a method and apparatus for separating of combustible and/or condensable and/or precipitable substances possibly being harmful from waste gases of drying plants.
2. Brief Description of the Background of the Invention Including Prior Art
Previously it had been found essential to cool waste gas so far until the volatile harmful substances are forced to condense and thereby deposit from the waste gas under formation of dust or the like. In the previous method and apparatus the applications were in particular but not exclusively in drying of wood chips where in addition to wood dust natural and synthetic resins and terpenes as well as water vapor are contained in the waste gas. In addition to this special application the previous process and apparatus can be also applied in such cases where similar waste gases are produced carrying comparable volatile substances such as for example in the drying of veneer, in the processing of lacquer and the like.
It is prevented by way of the method and apparatus previously found that harmful substances pass into the environment and at the same time there is a considerable saving of energy. The condensable harmful substances depositing under formation of dust or the like from the waste gas during the process of forced condensation cause the employed heat exchanger to clog up rapidly depending on the contents of dust in the waste gas. Therefore, a relatively frequent purification and cleaning of the heat exchanger is required. The previously found method and apparatus provide for cleaning by intermittently burning off the deposited substances. Apart form the fact that this method of cleaning can only be applied in cases where the deposited materials are to a large extent combustible there are considerable problems with the sealing, especially if the waste gas/volatile substances mixture has to be considered as possibly being subject to explosions. In addition, energy has to be provided for the burning off, which could be lost.